One of the best known forms of spatial light modulation of coherent light is the hologram in which a beam of coherent radiation is brought together with a spatially modulated coherent beam, with the result that the information is imparted to the previously featureless beam by modulation in space rather than be impingement on a transparency or other object. Since the early days of holography many efforts have been made to achieve spatial light modulation having the characteristic of real time modulation or modulation which is contemporary with the events causing the modulation. In spite of the efforts to obtain real time, reusable spatial light modulation the only successes have been unwieldy in nature, generally poor in quality and extremely expensive in actual use. The purpose of the present invention is to provide a way in which a coherent beam can be modulated by an incoherent light pattern readily and inexpensively in real time for such things as pattern recognition, for detection of size or orientation of an oject or image, for image enhancement of the like.